Effect of hybrid coagulation–membrane filtration on downstream UV disinfection

Recent studies have demonstrated the promising application of membrane filtration and UV disinfection in drinking water treatment. This research on virus removal originated from two important considerations: (i) reduced virus rejection following hydraulic backwash and (ii) UV disinfection can be adversely compromised by upstream treatment performance. The effect of upstream coagulation–membrane filtration on UV disinfection has not been well understood. This study therefore provides an investigation on this issue using a batch and continuous-mode system. For MF filtration, low MS2 rejections were observed initially, followed by gradual increase in rejections as filtration time increased. This adversely affected the UV dose requirements downstream when a specified log removal was to be attained by this hybrid membrane-UV disinfection system. Overall, UV disinfection efficacy of MS2-associated flocs was higher than unassociated-MS2. Inactivation (positive effect) by the presence of coagulants was more dominant than the negative effects of turbidity. Although it was anticipated that MS2 rejection might be compromised immediately following backwashing of MF, results did not indicate so. MS2 rejections initially fluctuated in the range of 86%–100%, and increased gradually to 100% as filtration time increased. Following hydraulic backwash, MS2 rejection still maintained consistent at 100%.

► High MS2 rejection by hybrid coagulation–MF/UF in the presence of turbidity.
► Likewise, higher UV inactivation rate K of floc-associated MS2.
► Enhanced MS2 inactivation due to floc enmeshment and UV light inactivation.
► Enhanced inactivation not due to synergy.
► Hydraulic backwash did not result in subsequent reduction in MS2 rejection.